In order to have a smaller unit recording area and promote higher storage capacity, hard disk drives having lower flying height of the magnetic head have been desired. In order to lower the flying height of the magnetic head, the surface smoothness of the hard disk substrate has become increasingly important. So far, the surface smoothness has been evaluated by surface roughness as determined by a profilometer having a diameter of 0.2 μm and a cut off of 25 μm (wavelength: 0.2 to 25 μm), and microwaviness as determined by cut-off of 800 μm (wavelength: 0.2 to 800 μm), and reduction in the surface roughness and the microwaviness have been tried.
As a method for manufacturing a substrate in need of surface smoothness as evaluated by the surface roughness and the waviness as described above, mechanical conditions such as control of the pore size of the polishing pad, control of the hardness, and control of the polishing load or rotational speed during polishing have been studied. On the other hand, as the process for improving the polishing composition and the polishing process, in Japanese Patent Laid-Open No. Hei 11-10492, a method including the steps of carrying out a polishing process by a plurality of steps, polishing with a polishing composition containing metal oxide abrasive grains having a particle size of from 0.3 to 5 μm before final polishing, and further polishing with a polishing composition containing a colloidal particle having a particle size of from 0.01 to 0.3 μm has been studied.